title: MNU-induced rat mammary carcinomas: immunohistology and estrogen receptor expression.
abstract: Environmental exposure to nitrosamines is associated with the development of cancer in a variety of target organs. One such carcinogen, N-methyl-N-nitrosurea (MNU), has long been used to induce mammary tumors in rats, which provide a useful model to study mammary carcinogenesis. However, some poorly clarified issues remain, such as the lack of a clear description of morphological patterns of tumors and the distribution and role of estrogen receptors (ERs) during tumor progression, as tumors overexpressing ERs show a paradoxical tendency to recur after ovariectomy. Mammary carcinomas were induced in Sprague-Dawley rats using MNU. The tumors were studied histologically and distribution of smooth muscle actin and ERs was studied immunohistochemically. All tumors presented both an epithelial and a myoepithelial component, demonstrated by immunohistochemical detection of smooth muscle actin. Tumors showed distinct histological patterns: well-differentiated papillary and adenoid areas and poorly differentiated solid and spindle-cell foci. Overexpression of ERs (>75% of labelled cells vs. 0-75% in control tissue) occurred in papillary and adenoid areas but not in solid and spindle-cell foci. Poorly differentiated tumor foci are likely to represent a more advanced, estrogen-independent phase in cancer progression and constitute the basis for tumor recurrence after ovariectomy.
authors.affiliation: Abel Salazar Institute for Biomedical Sciences, University of Porto, Porto, Portugal.
authors.forename: R
authors.initials: R
authors.lastname: Soares-Maia
authors.forename: A
authors.initials: A
authors.lastname: Faustino-Rocha
authors.forename: C
authors.initials: C
authors.lastname: Teixeira-Guedes
authors.forename: J
authors.initials: J
authors.lastname: Pinho-Oliveira
authors.forename: D
authors.initials: D
authors.lastname: Talhada
authors.forename: A
authors.initials: A
authors.lastname: Rema
authors.forename: F
authors.initials: F
authors.lastname: Faria
authors.forename: M
authors.initials: M
authors.lastname: Ginja
authors.forename: R
authors.initials: R
authors.lastname: Ferreira
authors.forename: R
authors.initials: R
authors.lastname: da Costa
authors.forename: Paula A
authors.initials: PA
authors.lastname: Oliveira
authors.forename: C
authors.initials: C
authors.lastname: Lopes
mesh_terms: D000199:Actins / Q000378:metabolism; D000230:Adenocarcinoma / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology*; D000818:Animals; D002273:Carcinogens / Q000633:toxicity; D002454:Cell Differentiation; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology*; D008770:Methylnitrosourea / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011960:Receptors, Estrogen / Q000378:metabolism*
chemical_list: D000199:Actins; D002273:Carcinogens; D008770:Methylnitrosourea; D011960:Receptors, Estrogen; C498862:Acta2 protein, rat